The present invention relates generally to the centering of logs in a veneer lathe charger to obtain an optimum yield of wood veneer from such logs when they are peeled in a veneer lathe and, in particular, to methods of centering a log in a veneer lathe charger which includes scanning the log during rotation and lateral movement of such log toward a transfer position while it is engaged by spindles, determining the optimum yield axis from the scan data, and adjustment of the spindles to align the optimum yield axis with a lathe reference axis at such transfer position for transfer to the veneer lathe axis.
It has been previously proposed in U.S. Pat. No. 3,852,579 of Sohn, et al., issued Dec. 3, 1974, to provide a computer-controlled veneer lathe charger for centering logs using light reflection scanning as the logs are rotated by spindles to determine the surface configuration of the logs. The log spindles are not moved laterally during scanning but are adjusted by a digital computer control system to reposition the log subsequent to scanning after the computer determines the optimum spin axis of the log from the scan data.
In a veneer lathe charger manufactured by The Coe Manufacturing Company, Painesville, Ohio, the logs are first rough-centered mechanically by three centering arms at each end of the log and then rotated by spindles about the rough center axis while scanning to determine the optimum yield axis of the log with a computer, as shown in U.S. Pat. No. 4,197,888 of McGee, et al., issued Apr. 15, 1980. After scanning, the spindles on which the log is rotated are adjusted horizontally and vertically to reposition the log until its optimum yield axis is aligned with a lathe reference axis at a transfer position. The aligned log is engaged by support arms, such as pendulum arms, at the transfer position for transfer of the log from the lathe charger to the veneer lathe axis for peeling. To avoid the high cost of mechanical centering, it has been previously proposed in the Type 784 lathe charger of Coe to rough-center the log by first scanning the log in a rest position with light sensors to determine its approximate center axis. The log is moved from the rest position to a rotating scan position where the ends of the log are engaged with spindles at such approximate center axis and then the log is rotated on such spindles during a second scanning to determine its optimum yield axis. After this scanning, the spindles are adjusted to align the optimum yield axis and the log is moved to a transfer position. Unfortunately, movement from the rest position to the rotating scan position takes a long time, thereby reducing the number of logs which can be centered in a given time period.
The above problems are overcome by the method of centering a log in a veneer lathe charger in accordance with the present invention. The approximate center axis of the log is determined by scanning the log while it is in a rest position as the spindles are lowered toward the rest position to determine its approximate center axis. The spindles engage the opposite ends of the log at such approximate center axis for rotation of such log. Then, the log is scanned with light sensors or other noncontact scanners as such log is being rotated and moved laterally from the rest position upward toward a transfer position. During lateral movement of the log toward the transfer position, the optimum yield axis of the log is determined from the scan data and the spindles are adjusted to align the optimum yield axis with a lathe reference axis at the transfer position for transfer to the veneer lathe axis. This method is extremely efficient in reducing the amount of time required for centering and in producing accurate centering. Thus, in one embodiment of the invention, 15 log blocks a minute can be centered, or one block every 4 seconds, which is an increase in production of approximately 25 percent over prior methods which scan the log as it is being rotated without any lateral movement of the log during scanning, as is done in the assignee's Type 784 lathe charger.
It has previously been proposed in U.S. Pat. No. 4,248,532 of Nosler, issued Feb. 3, 1981, to scan logs with image displacement-type light reflection scanners spaced longitudinally along the log. These light-reflection scanners are preferably used for the scanning steps in the method of the present invention for greater accuracy. However, other types of noncontact scanning can also be employed, including shadow or occlusion light scanning such as shown in U.S. Pat. No. 4,197,888 of McGee, issued Apr. 15, 1980, or acoustical scanning using ultrasonic transducers, as shown in U.S. Pat. No. 4,412,297 of Halgrimson, et al., issued Oct. 25, 1983.
Also, the lathe charger and method of the present invention uses a "Singulator" type of log conveyor device for separating logs, for feeding them one at a time into the rest position where they are rough scanned, and for discharging any rejected logs in a rapid, simple, and trouble-free manner. As shown in U.S. Pat. No. 4,245,735 of Valo issued Jan. 20, 1981, such Singulator devices have previously been used for transferring logs but not to support a log in a lathe charger while the log is being rough-scanned in the manner of the present invention.